Fabrication method and apparatus using ferrite for shifting phase of an electromagnetic wave

ABSTRACT

The present invention relates to an apparatus and method of manufacture of a simple and inexpensive ferrite phase shifter. It is economical to have the ferrite bar with its concommitant longitudinal rectangular hole for the high dielectric constant insert to be fired in the desired shape but it is rather difficult to hold the high tolerance of flatness required to fit the precision waveguide housing normally used. The &#39;&#39;&#39;&#39;as fired&#39;&#39;&#39;&#39; ferrite bars are often slightly warped or have a slight twist and likewise the hole generally follows the distortions of the entire ferrite bar, i.e., the hole is not perfectly straight. From the electrical point of view, a slight warpage in the bar is not in itself detrimental. It is undesirable only because it cannot be accurately fitted to the waveguide housing. These and other problems are circumvented by wrapping a metallic foil around a composite structure comprised of the ferrite bar and side spacers of low dielectric constant to form the phase shifter.

United States Patent [1 1 Ajoika et al.

FABRICATION METHOD AND APPARATUS USING FERRITE FOR SHIFTING PHASE OF AN ELECTROMAGNETIC WAVE Inventors: James S. Ajioka; William R. Barten, both of Fullerton, Calif.

Hughes Aircraft Corporation, Culver City, Calif.

Filed: July 27, 1972 Appl. No.: 275,841

Assignee:

References Cited UNITED STATES PATENTS 10/1968 Heiter 333/24.1 12/1965 Heithaus 333/24.l X 2/1968 Jones et al. l 333/24.l 11/1971 Lavedan, Jr. 333/24.l UX

DlELECTRlC SPACERS 13,14

FERRITE BAR 1O Sept. 25, 1973 Primary Examiner-Paul L. Gensler AIt0rney-W. H. MacAllister, Jr. et al.

[57] ABSTRACT The present invention relates to an apparatus and method of manufacture of a simple and inexpensive ferrite phase shifter. It is economical to have the ferrite bar with its concommitant longitudinal rectangular hole for the high dielectric constant insert to be tired in the desired shape but it is rather difficult to hold the high tolerance of flatness required to fit the precision waveguide housing normally used. The as fired ferrite bars are often slightly warped or have a slight twist and likewise the hole generally follows the distortions of the entire ferrite bar, i.e., the hole is not perfectly straight. From the electrical point of view, a slight warpage in the bar is not in itself detrimental. It is undesirable only because it cannot be accurately fitted to the waveguide housing. These and other problems are circumvented by wrapping a metallic foil around a composite structure comprised of the ferrite bar and side spacers of low dielectric constant to form the phase shifter.

3 Claims, 13 Drawing Figures METAL HOUSING Patented Sept. 25, 1973 5 Sheets-Sheet 1 Fig. l.

Fig. 2.

Patented Sept. 25, 1973 3,761,845

I 5 Sheets-Sheet 15 F Fig. 8.

Fig.9.

Patented Sept. 25, 1973 3,761,845

5 Sheets-Sheet 4 Fig.10.

Fig.11.

Patented Sept. 25, 1973 5 Sheets-Sheet METAL HOUSING m B S R E m P S DIELECTRIC FABRICATION METHOD AND APPARATUS USING FERRITE FOR SHIFTING PHASE OF AN ELECTROMAGNETIC WAVE BACKGROUND OF THE INVENTION It is the present practice to implement a ferrite phase shifter by accurately fitting a ferrite bar inside a waveguide. It is well known that the most critical tolerance in waveguide ferrite phase shifters is the contact between the waveguide and ferrite surface. Typically, air gaps between the ferrite and waveguide of greater than 0.0005 inches can cause the generation of undesirable higher order modes which cause radio frequency loss resonances to occur. In the past, the intimate contact was assured by extremely accurate grinding of the ferrite surfaces to maintain perfect flatness fo the top and bottom surfaces that must contact the waveguide. Also, the waveguide itself must be accurately ground to mate with the ferrite bar. If the waveguide housing is too loose, loss resonances can occur and if it is too tight undesirable magnetostriction effects can occur. This accurate grinding and accurate fitting of the ferrite bar to the waveguide is costly in production. In addition, the assembly process is rather difficult.

Thus, summarizing, the ferrite bar must be accurately ground to high dimensional tolerance and flatness. This is not only costly but may cause the hole in the bar, which is fired in" and bends with the bar, to be off center rendering the unit useless. Next, the waveguide holder must be machined accurately to mate with the ferrite bar without being too tight to cause magnetostriction effects. Lastly, the assembly of the phase shifter is difficult. This is especially true in threading the drive wires without breakage or without causing short circuits to the waveguide walls during insertion of the ferrite bar into'the waveguide.

SUMMARY OF THE INVENTION In accordance with the present invention, an economical ferrite phase shifter is provided by wrapping a metallic foil around a composite structure comprised of the ferrite bar and two side spacers of low dielectric constant. The side spacers are of such a width that the entire structure has the same cross section as the desired waveguide housing. The composite structure is glued together with low loss glue. When this structure is wrapped with foil, the foil becomes the waveguide. Sincethe foil is resilient, it can follow the contour of the as fired ferrite bar even if it is slightly warped or twisted. Thus intimate contact of waveguide and ferrite is assured. The wrapped device is then inserted in a holding device which protects the phase shifter and provides means for attaching to other waveguides.

The net result in that accurate grinding of the ferrite and the accurately machined waveguide are eliminated-both of which are very costly. In addition, there will be less attrition in ferrite bars because of the obvious possibility of cracking, chipping, or contaminating the ferrite bar during the grinding process. Also, since the hole in the ferrite usually follows the outer contour of the as tired" ferrite it can remain centered at all cross sections whereas if the outer surface is ground flat, the hole will become off-center at various cross-sections making the bar useless. Another advantage of the foil wrapping technique is that the difficulty of threading the drive wires through the holes in a precision waveguide is eliminated. In the foil wrapped method, the drive wires are all simultaneously inserted in matching holes in the falt foil before the wrapping operation. This has the further advantage that the wires make the foil and ferrite bar self jigging in that the proper alignment'of the flat foil and ferrite bar is automatically assured.

BRIEFDESCRIPTION OF THE DRAWINGS I FIG. 1 shows a perspective view of the device of the present invention without protective and connecting apparatus;

FIGS. 2-4 illustrate the disadvantages of grinding versus the use of foil;

FIG. 5 illustrates apparatus for implementing a process for fabricating the device of FIG. 1;

FIGS. 6-10 illustrate the process for fabricating the device of FIG. 1;

FIG. 11 shows the device of FIG. 1 being inserted in a protective device;

FIG. 12 illustrates a perspective view of the device of FIG. 1 in a protective and connecting apparatus; and

FIG. 13 shows a cross-sectional view of the device of FIG. 12.

DESCRIPTION Referring to FIG. 1 of the drawings, there is shown the essential portions of the ferrite phase shifter of the present invention from the standpoint of electronic operation. In particular, a ferrite bar 10 of rectangular cross-section extends for the entire length of the phase shifter. The ferrite bar 10 is fired" with a rectangular hole 12 which runs lengthwise therethrough and is centrally disposed with the longer axis thereof coinciding with the longer axis of the cross-section of bar 10 and the shorter axis coinciding with the short axis of the bar 10. The ferrite of bar 10 is of a type that is commercially available and has a relative dielectric constant that is of the order of 16. Low dielectric spacer bars 13, 14 each ofa width equal to that of ferrite bar 10 are disposed coextensively on both sides thereof and glued in place with low loss glue. Spacer bars 13, 14 are preferably of equal thickness to form a composite bar 15 having cross-sectional dimensions equal to the desired inside dimensions of waveguide to be used along the ferrite phase shifter. The low dielectric spacer bars 13,14 are fabricated from commercially available dielectric foam having a dielectric constant of the order of 2. By having a low dielectric constant is meant that the dielectric constant is low compared to the dielectric constant of the ferrite bar 10 which has a constant of the order of sixteen. An alternative configuration would be to make the low dielectric spacer bars 13,14 hollow so that the composite dielectric constant would approach that of air. The waveguide about composite bar 15 is provided by a sheet of foil 16 of a width equal to that of the length thereof and wrapped thereabout and joined along the center of a broad side of low dielectric spacer bar 13 by means of a soft solder joint 17. Drive wires 18,19,20 are disposed through the opposite side of composite bar 15 and foil 16 to the rectangular hole 12 and extend for predetermined portions therealong. The ratio 4:2:1 is typical for the lengths of the drive wires. The rectangular hole 12 is then filled with a commercially available high dielectric core 21 which has a relative dielectric constant of the order of 30. It

has been found that the dielectric core 21 may have a dielectric constant that ranges from a constant greater than that of ferrite bar 10 to a constant of the order of 38. By high is meant that the dielectric constant of core 21 is high compared to the dielectric constant of the ferrite bar 10 which is of the order of 16. The method of constructing the foregoing portions of the ferrite phase shifter is described in connection with FIGS. 5 through 10.

Referring to FIG. 2 there are shown side and end views of a ferrite bar having a fired in rectangular hole 12 that is warped. From the electrical point of view, a slight warpage of the bar 10 is not in itselfdetrimental. It is bad only because it cannot be accurately fitted to the waveguide housing. Also, when the outer surfaces of the ferrite bar 10 are ground flat, the center hole 12, which cannot be straightened, often becomes sufficiently off-center (at various cross-sections) to render the bar 10 electrically useless as evident in FIG. 3. The present method of fabricating a ferrite phase shifter does not require grinding in the manner shown in FIG. 3 but rather utilizes a sheet of foil 16 which follows the contour of the as tired ferrite bar 10 as shown in FIG. 4. The rectangular hole 12 remains centered along the length of bar 10 whereby warppage does not detrimentally affect the electronic performance of the ferrite phase shifter. It is to be understood, of course, that the ferrite bar 10 is not intentionally warped or twisted but may become that way during the manufacturing processes.

Referring to FIG. 5 there is shown an exploded view of apparatus for implementing a method for assembling the ferrite phase shifter of FIG. 1. In particular, the apparatus of FIG. 5 includes a vertical traverse rod 30 supported by a stand 32. A support block 34 is attached to the vertical traverse rod 30 by means of a slidable bracket 35. Support block 34 includes holes 34-41 that are placed to accommodate the drive wires 18,19,20 and has a substrate area that is exactly coextensive with the broad side of ferrite bar 10 and the low dielectric spacer bars 13,14, i.e., the composite bar 15. The sheet of foil 16 which is preferably aluminum or copper initially has a width sufficient to wrap around the composite bar with a slight overlap along the center of low dielectric spacer bar 13. The overlapped portions of the sheet of foil 16 are pre-tinned so that they may be subsequently soldered together. Further, the sheet of foil 16 is pre-cut with the edges along the broad sides of the low dielectric spacer bars 13,14 coextensive with the edges thereof and the edges along the remaining sides of composite bar l5 cut to extend longer than the bar 15. Holes are punched along the center of the sheet of foil 16 to coincide with the holes in low dielectric spacer bar 14 for the drive wires 18,19 and 20.

The pre-cut punched sheet of foil 16 is then placed over the support block 34 with the holes therethrough coinciding with corresponding holes 36-41. The drive wires 18,19,20 are threaded through appropriate holes in composite bar 15 along rectangular hole 12. The threaded composite bar 15 with the drive wires 18,19,20 down, as shown in the drawing, is then placed over the sheet of foil 16 coextensive with the support block 34 and with the drive wire 18 extending through holes 36,37; the drive wire 19 extending through holes 38,39; and the drive wire 20 extending through holes 40,41.

A pressure device 44 having a flat under-surface of an area that is the same lenth but somewhat narrower than the top surface of composite bar 15, as shown in FIG. 5 of the drawings, is supported on top of composite bar 15 by means of a bracket 45 which, in turn, is attached to a slidable mounting 46 on the vertical traverse rod 30. A heating element 47 is disposed along the center of the underside of pressure device 44 flush with the surface thereof. Directly below the support block 34 is placed a nylon or teflon U-shaped forming block 50 which is held in place by means of a vise 52 which is attached to the stand 32. The channel of the U-shaped forming block 50 has a depth equal to the vertical dimension of support block 34 and composite bar 15, as shown in FIG. 5. Further, the corners of forming block 50 at the top of the channel are rounded to provide a guide for the insertion of the support block 34, sheet of foil 16 and composite bar 15, as will be hereinafter explained.

FIGS. 6-10 illustrate cross-sectional views of the apparatus of FIG. 5 during the process of forming the ferrite phase shifter in the form shown in FIG. 1. Referring to FIG. 6 the pressure device 44 is dropped down into actual contact with the composite bar 15 which rests over the support block 34 with the pre-cut pre-tinned sheet of copper foil 16 inbetween. The support block 34 along with composite bar 15 and pressure device 44 is moved directly over the channel of the U-shaped forming block 50 and lowered to the bottom thereof as shown in FIG. 7 of the drawings. This operation folds the sheet of foil 16 over both sides of the composite bar 15 leaving the exposed surface thereof flush with the top surface of forming block 50.

Proceeding to FIG. 8, an inverted nylon or teflon U- shaped forming block 54 is used to finish wrapping the sheet of foil 16 about the composite bar 15. The channel depth of U-shaped forming block 54 is not critical but should be greater than the height of the unfolded sheet of foil 16 above the top surface of block 50. The inner edges of the block 54 are rounded so as to avoid shearing the sheet of foil 16. The left side of forming block 54 is then placed over the left side of forming block 50, as shown in the drawing, and is then pulled to the right while applying moderate pressure. The direction of forming block 54 is then reversed, as shown in FIG. 9, and the remaining portion of the sheet of foil 16 wrapped around the composite bar 15. Next, as shown in FIG. 10, the pressure device 44 is positioned over the wrapped composite bar 15 and the heating ele merit 47 energized sufficient to melt the solder of the pre-tinned surface and then de-energized to allow the solder to solidify while holding the sheet of foil 16 in position. The wrapped composite bar 15 may now be removed from the forming block 50.

The foil wrapped ferrite phase shifter of FIGS. 1 and 10 is not practicable for use in an electronic system in the state shown as it is too fragile and has no way of coupling from and to waveguide in the system. A housing for protecting the ferrite phase shifter and at the same time providing a means to couple to external waveguide is described in connection with FIGS. 11, 12 and 13. Referring to FIG. 11 waveguide flanges 60,62 are spaced a distance apart exactly equal to that of the composite bar 15. Each of the flanges 60,62 includes a square and/or rectangular aperture ofa size to just receive the foil wrapped composite bar 15. In addition, one of the flanges or 62 such as flange 60 includes a notch 63 in the center of the side designed to be adja cent the low dielectric spacer bar 14 to allow for passage of the drive wires 18,19,20 when the foil wrapped composite bar of FIG. is slid through the flange 60. The flanges 60,62 are connected by a flat metal bar 64 which extends between and is flush with the respective opposite edges of the apertures therein. In addition, flat metal bars 65,66 extend between flanges 60,62 on both sides of the notch 63 and are flush with the sides of the apertures therein opposite from the flat metal bar 64. The foil wrapped composite bar with the drive wires 18,19,20 may now be slid inbetween the flat metal bar 64 and the flat metal bars 65,66 with the drive wires 18-20 passing through the notch 63. It is, of course, possible to assemble the flange 60 onto the flat metal bars 64,65,66 last so that notch 63 is not required.

Referring now to FIGS. 12,13 ears of the sheet of foil 16 extending out from the composite bar 15 are folded back on the flat surface of the flanges 60,62 and conductively attached thereto. A series of phosphor bronze finger springs 70,72 with wrap-around ends are now connected across the flat metal bars 64,65 and across the flat metal bars 64,66, respectively. A cylindrical metal housing 76 of an inside diameter equal to the diameter of the flanges 60,62 is then disposed about the ferrite phase shifter from the flange 60 to the flange 62 whereby the springs 70,72 support the foil wrapped composite bar 15 along the entire length thereof. In actual operation, it may be desirable to circulate coolant on the outside of cylindrical metal housing 76 whereby connections to the drive wires 18,19,20 may be made through the flanges 60 or 62 and the mating flange in the electronic system.

What is claimed is:

1. A ferrite phase shifter adapted to connect to rectangular waveguide of predetermined height and width, said ferrite phase shifter cmprising a ferrite bar of predetermined dielectric constant having a rectangular cross-section with a fired-in rectangular hole disposed longitudinally therethrough, the width of said ferrite bar being equal to said predetermined height; first and second low dielectric spacer bars of the same rectangular cross-section disposed coextensively adjacent both broad sides of said ferrite bar thereby to form a composite bar with said first and second sapcer bars having a combined thickness equal to said predetermined width less the height of said ferrite bar; a sheet of metallic foil disposed completely around the entire length of said composite bar in close proximity thereto thereby to provide a foil wrapped composite bar, said sheet of metallic foil having ears at the extremities of said composite bar on the sides thereof in contact with said ferrite bar; first and second flanges disposed about opposite extremities of said foil wrapped composite bar with said ears folded back and conductively attached thereto; a first rigid flat bar extending between aid first and second flanges adjacent to and co-extensive with said first spacer bar of said foil wrapped composite bar; second and third rigid flat bars extending between said first and second flanges adjacent to and co-extensive with said second spacer bar of said foil wrapped composite bar, said second and third rigid flat bars having an intervening space along the central portion of said second spacer bar of said foil wrapped composite bar; and no less than one driver wire penetrating into and extending along said rectangular hole through said foil wrapped composite bar at first and second places along said central portion of said second spacer bar; and a dielectric material within said rectangular hole of said ferrite bar, said dielectric material having a dielectric constant greater than said predetermined dielectric constant.

2. The ferrite phase shifter as defined in claim 1 additionally including spring means extending between said first and second and between said first and third rigid flat bars for supporting said foil wrapped composite bar along the entire length thereof.

3. The method of fabricating a ferrite phase shifter using a ferrite bar of rectangular cross-section having an as-fired longitudinal hole therethrough, said method including placing low dielectric spacer bars flush with both broad sides of said ferrite bar to form a composite bar, threading no less than one drive wire through one of said spacer bars along said longitudinal hole and out through one of said spacer bars, and wrapping a sheet of metallic foil around the entire length of said composite bar in close proximity thereto with said drive wires penetrating therethrough including providing a sheet of foil at least as long as said composite bar and of a width greater than the perimeter of the crosssection thereof, placing holes in said sheet of metallic foil in positions to accommodate said drive wires, supporting said sheet of foil and said composite bar with said drive wires disposed through corresponding holes therein, folding said sheet of foil up the sides of said composite bar, folding opposite sides of said sheet of foil over the top of said composite bar, and electrically connecting said opposite sides of said sheet of foil together while simultaneously holding said sheet of foil snug against said composite bar.

zg g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,761,845 Dated September 25, 1973 Inventor) James S. Ajioka and William R. Barten It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cover page, directly beneath "United States Patent [19] Ajoika et al. should be: I

Ajioka et al.-

Signed and sealed this 11pm day of May 197E.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents- EDWARD H .FLETCHER,JR. Attesting Officer 

1. A ferrite phase shifter adapted to connect to rectangular waveguide of predetermined height and width, said ferrite phase shifter cmprising a ferrite bar of predetermined dielectric constant having a rectangular cross-section with a fired-in rectangular hole disposed longitudinally therethrough, the width of said ferrite bar being equal to said predetermined height; first and second low dielectric spacer bars of the same rectangular cross-section disposed coextensively adjacent both broad sides of said ferrite bar thereby to form a composite bar with said first and second sapcer bars having a combined thickness equal to said predetermined width less the height of said ferrite bar; a sheet of metallic foil disposed completely around the entire length of said composite bar in close proximity thereto thereby to provide a foil wrapped composite bar, said sheet of metallic foil having ears at the extremities of said composite bar on the sides thereof in contact with said ferrite bar; first and second flanges disposed about opposite extremities of said foil wrapped composite bar with said ears folded back and conductively attached thereto; a first rigid flat bar extending between aid first and second flanges adjacent to and co-extensive with said first spacer bar of said foil wrapped composite bar; second and third rigid flat bars extending between said first and second flanges adjacent to and co-extensive with said second spacer bar of said foil wrapped composite bar, said second and third rigid flat bars having an intervening space along the central portion of said second spacer bar of said foil wrapped composite bar; and no less than one driver wire penetrating into and extending along said rectangular hole through said foil wrapped composite bar at first and second places along said central portion of said second spacer bar; and a dielectric material within said rectangular hole of said ferrite bar, said dielectric material having a dielectric constant greater than said predetermined dielectric constant.
 2. The ferrite phase shifter as defined in claim 1 additionally including spring means extending between said first and second and between said first and third rigid flat bars for supporting said foil wrapped composite bar along the entire length thereof.
 3. The method of fabricating a ferrite phase shifter using a ferrite bar of rectangular cross-section having an ''''as-fired'''' longitudinal hole therethrough, said method including placing low dielectric spacer bars flush with both broad sides of said ferrite bar to form a composite bar, threading no less than one drive wire through one of said spacer bars along said longitudinal hole and out through one of said spacer bars, and wrapping a sheet of metallic foil around the entire length of said coMposite bar in close proximity thereto with said drive wires penetrating therethrough including providing a sheet of foil at least as long as said composite bar and of a width greater than the perimeter of the cross-section thereof, placing holes in said sheet of metallic foil in positions to accommodate said drive wires, supporting said sheet of foil and said composite bar with said drive wires disposed through corresponding holes therein, folding said sheet of foil up the sides of said composite bar, folding opposite sides of said sheet of foil over the top of said composite bar, and electrically connecting said opposite sides of said sheet of foil together while simultaneously holding said sheet of foil snug against said composite bar. 